1. Field of the Invention
The present invention relates to ethylene copolymers derived from ethylene and at least two different alkyl acrylates comonomers, with or without additional comonomer containing acid cure sites, which exhibit lower glass transition temperatures (Tg) and also relates to compounded compositions and cured vulcanizates using these copolymers and rubber articles manufactured therefrom, which exhibit improved low temperature properties yet maintain the good heat and fluid resistance of previous ethylene copolymers comprising a single alkyl acrylate comonomer. More specifically, but not by way of limitation, the present invention relates to ethylene terpolymers optionally containing a fourth cure site containing monomer (for example, ethylene/methyl acrylate/n-butyl acrylate/ethyl hydrogen maleate) and fabricated rubber articles derived therefrom (e.g., ignition wire jacketing, hoses, dampers, seals, gaskets, spark plug boots, constant velocity joint boots and shaft boots).
2. Description of the Related Art
The automotive and transportation industries use elastomeric (rubber-like) materials for a number of parts that require elastic properties such as gaskets, seals, hoses, dampers, etc. These parts require good heat and oil swell resistance. A number of synthetic polymeric materials have been provided for these applications.
U.S. Pat. Nos. 3,883,472 and 3,904,588 disclose ethylene/acrylic ester/butenedioic acid monoester terpolymers, compounds and vulcanizates thereof.
U.S. Pat. No. 5,498,669 discloses blends of ethylene/alkyl acrylate dipolymers, neutralized ethylene acid copolymers (ionomers) and organic peroxides, useful for continuous pressureless curing processes.
The compounds of the ethylene/alkyl acrylate copolymers and blends described in U.S. Pat. Nos. 3,883,472; 3,904,588 and 5,498,669 have very good resistance to both heat and fluid, and when plasticized are disclosed to have brittle points below −40° C., as measured by ASTM D746-70. These prior art copolymers have polymer glass transition temperatures (Tg) by differential scanning calorimetry (DSC) of −21 to −30° C., ASTM method E1356-98 (using the inflection point as Tg).
However, trends in the automotive industry are simultaneously towards higher under-hood temperature, use of new fluids for improved vehicular performance and longer parts service life, which requires lower temperature capability of the elastomer system. These trends are driven by new environmental regulations, market demands for better fuel economy, and longer warranties offered by automotive manufacturing companies. As a result, elastomeric materials used in making automotive parts (gaskets, seals, hoses, dampers, etc.) are required to have wider ranges (both high and low) of service temperature capabilities and good fluid resistance to meet the new design demands. Such a combination of properties and moderate cost are highly desired.